1. Field of the Invention
The present invention relates to protective eyewear. More specifically, the present invention relates to such eyewear satisfying eye-safety criteria set forth by the Occupational Safety and Health Administration (OSHA) and by the American National Standards Institute (ANSI). More specifically yet, the present invention relates to such eyewear, a part of which provides the user a visual correction and/or enhancement.
2. Description of the Prior Art
Traditionally, neither magnifiers or prescriptive lenses have been readily available for protective eyewear. Consequently, people using such protective eyewear often have to switch back and forth between their protective eyewear and their corrective eyewear to carry out their task. This is especially true for those persons needing near-point correction, the function of "reading glasses." As this practice of switching glasses is a continual nuisance, dangerous to the wearer, and explicitly against OSHA regulations in certain settings, there has been an increasing demand for protective eyewear for sports, welding, machine shop work, and the like, that meet the specific visual needs of the wearer, thus relieving the wearer of the need to continually switch glasses.
As stated, a set of "reading glasses " has as its function the correction of (or, better stated, compensation for) its user's near-point --definable as the closest point to a person's eyes to which an object can be brought and on which object the person is still able to focus his or her eyes. The ability to bring such things into focus depends on the ability of certain eye muscles to bring the radius of curvature of the eye's lens to a certain range; the closer the object to be focused, the smaller the lens' radius of curvature must be. Printed letters and numbers normally must be brought to within a reasonably dose distance to a person's eyes in order to appear large enough to that person so that he or she is able to identify what is written. For the vast majority of people, including those requiring no visual correction in their younger years, the lessening flexibility of the eyes' lens with age means that most people reach a point of no longer being able to focus on objects at near distances. That is, the near-point recedes; as a result, text that once could be read without glasses appears blurred and is impossible to read. The near-point distance, which starts out at a couple of inches during childhood in one with normal eyes, eventually moves out to a distance of 30 or 40 inches, where it stabilizes.
Reading glasses have simple convex lenses that permit an object held near enough for reading to actually appear to the eye's focusing mechanism as lying out at or beyond the user's near-point. (One says that the lenses form an "image" at or beyond the user's near-point.) Simply stated, the lenses focus an image as if the image is at or beyond the near-point, yet the image has the apparent size associated with it being much closer. The lens equation is (1/s)+(1/s')=1/f, where s is the distance of the object in front of the lens, s' is the distance of the image behind the lens, and f is the focal length of the lens. In the case of eyeglasses, the image will be on the same side of the lens as the object and hence will have a negative sign. Consider a person whose near-point is at a distance of 30". For reading, one typically holds the text about 10' in front of the eyes (taken to be at the same location as the eyeglasses). Thus, the lens formula for this person will take the form (11/0")-(1/30")=1/f Solving the equation for "f" yields f=15". Thus, 15" is the focal length required of lenses to enable a person to focus properly on letters or small objects at a typical "reading" distance.
Reading glasses will "work" just as long as they focus the image at or beyond the person's near-point. Thus, there is no need for precision in this type of eye correction. Because of this and the near-universal need for reading glasses, reading glasses have become commodities purchasable off the rack in variety stores and drug stores. They are sorted by "strength." The lower the focal length, the higher the strength, thus stated because the lower the focal length, the farther in front of the lens the image is formed. A person whose near-point has moved a long ways out needs glasses of great strength, sometimes called by the misnomer "magnification." On the rack, the quantity used to characterize the different glasses is a diopter number (or diopters). The diopter number of a lens is the reciprocal of its focal length stated in meters. Thus, a lens with a focal length of 15" or about 0.4 m has a diopter number of 2.5. It is a lens with a refractive strength of 2.5 diopters.
The commodity nature of reading glasses and the fact that this is by far the most common type of corrective eyewear that persons engaged in activities needing eye protection require, strongly suggests combining the commodity constituting protective eyewear with the commodity constituting reading glasses. The prior art, however, for the most part is directed to introducing into protective eyewear visual corrections specific to the individual who will be using the protective eyewear.
Although Fischer (U.S. Pat. No. 4,717,249 Issued 1988) teaches the provision of a reading-glass type lens in connection with a diving mask, there are severe limitations on that device. The lens-device is a combination of a refracting surface and a prism, so that the user of the diving mask, by glancing at the comer of the mask whereon the lens-device is contained, is able to see a watch or other object that is not in the direct line of sight through the lens. The refractory surface of the object also allows the viewer to focus on the watch or other object in such a way as to read text on the object. The lens-prism in Fischer is attachable to a diving mask, as basically an after-added feature. Fischer does not suggest providing masks with a series of lens-prisms with different diopter values. Also, it appears inherent in the device of Fischer that the lens-prism must be quite small, indeed too small, to allow a user to do much with the lens-prism facility other than to quickly glance at an instrument reading or the like.
Nix (U.S. Pat. No. 5,153,619 Issued 1992) discloses flexible, adhesive lenses having the standard range of diopter values. More specifically, the "device" of Nix is a card containing a series of such flexible, transferrable lenses ("flexlenses"), the best use of which would probably be in a machine shop or welding establishment employing a number of workers using standard protective eye protection. Each worker then could select the lens "strength" best suited for his near-point correction and affix those lenses to the protective eyewear he was going to use. The Nix "flexlens" is intended for use on all protective eyewear. Apart from the impermanence of the correction, a serious drawback of the Nix device is that the user is left to correctly position it upon the protective eyewear. A misplaced or accidentally wrinkled "flexlens" will render the corrected portion of the protective eyewear useless, and, at the very least, will result in the transference procedure having to be re-done.
Sved (U.S. Pat. No. 5,790,230 Issued 1998) teaches an eyeglass assembly that combines sport or safety glasses with detachable prescription lenses. The Sved device incorporates a flexible nose bridge that secures the right and left prescription lenses, and that attaches to an existing eyeglass frame such that the device is located between the inside protective surface of the protective eyewear and the user's eyes. In addition to the fact that the Sved approach to the problem, using the dual glasses, can result in clumsy eyewear, the prescription-glasses protective-eyewear combination of Sved may internally shift position during use, forcing the user to continually remove the dual glasses for adjustment
Therefore, what is needed is protective eyewear that incorporates in an integral way, the standard near-point corrective lens in such a manner that the user can alternately look at a distant object and at a dose-up object simply by slightly shifting the direction of his or her gaze. What is further needed is such protective eyewear having the corrective lenses set toward the lower portion of the eyewear, leaving the upper two-thirds of the user's field of vision protected but uncorrected. What is still further needed is such protective eyewear provided in a range of strengths similar to the strengths most common in reading glasses. Finally, what is needed is such protective eyewear that presents a cosmetically appealing appearance.